1. Field of the Invention
The present invention relates to a fuse structure and in particular a fuse structure that avoids damage from the laser blow process in its laser spot.
2. Description of the Related Art
Fuses are routinely used in the design of monolithic integrated circuits (IC), and particular in memory devices as elements for altering the configuration of the circuitry contained therein. As such, memories are commonly built with programmed capabilities wherein fuses are selectively “blown” by a laser beam.
It is well known that random access memories (RAM) are designed with redundancies which include spare columns, rows, or even fully functional arrays, such that when any element fails, the defective row, column and the like are replaced by a corresponding element. Disabling and enabling of spare elements are accomplished by fuses which are blown when required, preferably, by a laser beam.
Additionally, the technique of laser fuse deleting (trimming) has been widely used in both memory and logic IC fabrication industries, as an effective way to improve functional yields and to reduce development cycle time. Yet, fuse blow yield and fuse reliability are problematic in most conventional fuse designs.
FIG. 1 is a sectional view of a traditional fuse structure, FIG. 2 is a top view of a traditional fuse structure, and FIG. 1 shows a cross section C-C′ of FIG. 2.
Referring to FIG. 1, symbol 100 shows a substrate having a laser spot 110. A metal layer M0 is formed on part of the substrate 100. A metal layer M1 is formed on part of the oxide layer, between the metal layer M0 and metal layer M1 having a oxide layer 120. A conductive plug 130 to penetrate the oxide layer 120 electrically connected the metal M0 layer and M1 layer. A laser spot 110 on part of the metal M1 layer and the top of a part of the oxide layer 120 forms a fuse window 140. The symbol 150 is a passivation layer.
FIG. 2 is a top view of FIG. 1, showing a plurality of fuse structures 210, 220, 230, 240 in fuse window 140. Each fuse structure comprises an M0 layer, conductive plug 130 and M1 layer. The solid line area shows the M1 layer, the dashed line area shows M0 layer, and each fuse structure comprises its own optimal laser spot 11. To give an example, a laser beam 290 blows the position 110 of the fuse structure 220. Because of misalignment of the laser beam 290 or thermal scattering of the laser beam 290, thermal shock from the laser blow process can damage the M0 layer. This can cause cracking, seriously affecting device reliability, and yield.